Power system with zero voltage switching

ABSTRACT

A DC/DC converter includes first and second bridges comprising a plurality of switch elements and a plurality of coupling capacitors. Each coupling capacitor couples one of the switch elements of the first bridge to one of the switch elements of the second bridge. The first and second bridges are connected to a transformer comprising a first primary winding, a second primary winding, and a secondary winding. A coupled inductor comprises first and second inductors and is connected to the transformer so that the first and second primary windings are inductively coupled through the coupled inductor.

This application is a continuation of U.S. patent application Ser. No.10/152,883, filed May 21, 2002, which issued as U.S. Pat. No. 6,731,524,and which claims the benefit of U.S. Provisional Application Ser. No.60/292,350, filed on May 21, 2001. The entire disclosure of applicationSer. Nos. 10/152,883 and 60/292,350 are hereby incorporated into thepresent application by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention is generally directed to the field of power systems. Morespecifically, the invention is directed to power systems that generate aregulated constant output voltage. The invention is particularlyapplicable for use in the telecommunications industry and will bedescribed with particular reference thereto. It will be appreciated,however, that the invention has broader aspects and can be used forother purposes and in other industries.

2. Description of the Related Art

Power systems including regulated power systems are in widespread use ina variety of environments including power systems used in thetelecommunication industry. There is a general need for improvements invarious power systems, power circuits, and power components.

SUMMARY

A power rectifier includes a DC/DC converter. The DC/DC converterincludes first and second bridges comprising a plurality of switchelements and a plurality of coupling capacitors. Each coupling capacitorcouples one of the switch elements of the first bridge to one of theswitch elements of the second bridge. The first and second bridges areconnected to a transformer comprising a first primary winding, a secondprimary winding, and a secondary winding. A coupled inductor comprisesfirst and second inductors and is connected to the transformer so thatthe first and second primary windings are inductively coupled throughthe coupled inductor.

The power rectifier also includes a plurality of power supply units(“PSUs”). Each PSU has an output that is coupled to the output of otherPSUs in the power system. Each PSU comprises a first, second, and thirdpower train and a control assembly. Each power train comprises a powerfactor correction (“PFC”) circuit that receives an AC input andgenerates a first DC output and a DC/DC converter circuit that receivesthe first DC output and generates a second regulated DC output. Thecontrol assembly has a signal path to the first, second, and third powertrains. The control assembly monitors outputs supplied by the first,second, and third power trains and in response thereto provides controlsignals to each of the first, second, and third power trains.

The power rectifier also includes a plurality of control assembly inputcircuits, a signal processor, and a plurality of control assembly outputcircuits. The control assembly input circuits are operative to measurecharacteristics relating to each of the power trains and are operativeto generate a measured characteristics output. The signal processor isoperative to receive the measured characteristics output, performcomputations wherein the measured characteristics output is used in thecomputations, and generate a signal processor output. The plurality ofcontrol assembly output circuits are operative to generate error signalsbased on the signal processor output.

The power rectifier also includes an inductive coupler. An inductivecoupler comprises a first coil defining a first outer periphery and asecond coil defining a second outer periphery. A metal member extendsaround the first and second outer peripheries of the first and secondcoils forming a conductive loop.

The power rectifier also includes a phase controlled drive circuit. Thephase controlled drive circuit includes a drive circuit operable toprovide gate signals to an SCR bridge circuit and a phase controlcircuit. The phase control circuit includes a first phase generatoroperable to generate a first phase signal, and a second phase generatoroperable to generate a second phase signal. The second phase signal isperiodically reset to an initial value. A drive circuit actuator in thephase control circuit is operable to place the drive circuit in a firstactivation state when a sum of the first and second phase signalsexceeds a threshold value, and is further operable to place the drivecircuit in a second activation state when the sum of the first andsecond phase signals is less than the threshold value.

The power rectifier also includes a power factor correction circuit. Apower factor correction circuit includes a power circuit comprisingfirst and second input capacitors, first and second coupled inductors,first and second switches, and an output circuit. The first and secondinput capacitors form a bank node. The first and second switches areconnected to the first and second inductors and the bank node. Likewise,the first an second input capacitors are connected to the first andsecond inductors. The output circuit is operable to produce an outputvoltage. A control circuit is operable to monitor the output voltage andproduce a switch signal at a switching frequency. A drive circuit iscoupled to the control circuit and the first and second switches and isoperable to operate the first and second switches based on the switchsignal. The drive circuit and control circuit are connected to a flyingnode, the flying node at a common voltage at the switching frequency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an embodiment of a power supplyassembly;

FIG. 2 is block diagram illustrating connectivity of the power supplyunits used in the power supply assembly;

FIG. 3 is a block diagram illustrating the configuration of the powersupply unit;

FIG. 4 is a schematic diagram of a three phase power factor correctionassembly;

FIG. 5 is a schematic diagram of an alternate three phase power factorcorrection assembly;

FIG. 6 is a block diagram of an embodiment of the power factorcorrection assembly;

FIG. 7 is a block diagram of a power factor correction circuit;

FIG. 8 is a more detailed block diagram of a power factor correctioncircuit;

FIG. 9 is a schematic diagram of a power circuit;

FIG. 9A is a schematic diagram of an exemplary switch;

FIG. 10 is a schematic diagram of a switch control circuit;

FIG. 11 is a schematic diagram of a switch driver circuit;

FIG. 12A is a schematic diagram of an alternative embodiment of a powercircuit;

FIG. 12B is a schematic diagram of another alternative embodiment of apower circuit;

FIG. 13 is a schematic diagram illustrating a top view of an inductordevice having adjustable coupling between first and second coils;

FIG. 14A is a cross section view of the inductor device of FIG. 13;

FIG. 14B is a cross section view of the inductor device of FIG. 13, andfurther including an insulating material;

FIG. 14C is a cross section view of another embodiment of an inductordevice having adjustable coupling between first and second coils;

FIG. 14D is a cross section view of another embodiment of an inductordevice having adjustable coupling between first and second coils;

FIG. 14E is top view of another embodiment of an inductor device havingadjusting coupling between first and second coils;

FIG. 14F is a cross section view of another embodiment of an inductordevice having adjustable coupling between the first and second coils;

FIGS. 15-17 provides front, top and side views of an inductor devicehaving adjustable coupling between first and second coils;

FIGS. 18A and 18B provide a front and top view of an inductor devicewith an air core and having adjustable coupling between first and secondcoils;

FIG. 19 is a schematic diagram of a current doubler with a coupledinductor;

FIG. 20A is a schematic diagram of a bridge rectifier circuit used in aninrush limiting circuit;

FIG. 20B is a block diagram of the inrush limiting circuit;

FIG. 21 is a more detailed block diagram of the inrush limiting circuit;

FIG. 22A is a schematic diagram of an SCR drive circuit;

FIG. 22B is a schematic diagram of a phased soft start circuit and azero cross detection circuit;

FIG. 23 is a block diagram of series connected full bridge circuit;

FIG. 24 is a schematic diagram of an embodiment of the series connectedfull bridge circuit of FIG. 23;

FIG. 25A is a schematic diagram of the series connected full bridgecircuit during a first switch state;

FIG. 25B is a schematic diagram of the series connected full bridgecircuit during a second switch state;

FIG. 25C is a schematic diagram of the series connected full bridgecircuit during a third switch state;

FIG. 25D is a schematic diagram of the series connected full bridgecircuit during a fourth switch state;

FIG. 25E is a schematic diagram of the series connected full bridgecircuit during a fifth switch state;

FIG. 26 is a schematic diagram of another embodiment of the seriesconnected full bridge circuit of FIG. 23; and

FIG. 27 is a block diagram illustrating a preferred arrangement ofcomponents within a preferred power supply unit;

FIG. 28 is a block diagram illustrating a preferred DC/DC converter;

FIG. 29 is a schematic diagram of an exemplary DC/DC converter with acurrent sense circuit;

FIG. 30 is a block diagram that illustrates a preferred control topologyin a power supply unit;

FIG. 31 is a block diagram that illustrates a preferred control circuitin a DC/DC converter;

FIG. 32 is schematic diagram of a preferred control circuit in a DC/DCconverter;

FIG. 33 is a block diagram that illustrates a preferred digital controlassembly in a power supply unit;

FIGS. 34A, 34B, 34C, 34D, 34E, 34F, 34G, and 34H are schematic diagramsof exemplary circuits depicted in the block diagram of FIG. 33;

FIG. 35 is a flow chart of a preferred current balance algorithmexecuted by the digital control assembly;

FIGS. 36A & 36B are a block diagram of a preferred DSP circuit; and

FIG. 37 is a block diagram of a preferred DSP circuit.

DETAILED DESCRIPTION

FIG. 1 is a diagram illustrating an embodiment of a power supplyassembly 100 that is particularly useful in the telecommunicationsindustry. The preferred power supply assembly 100 comprises a powersupply enclosure 200, a power distribution assembly 210, a powerrectifier assembly 300, and a fan assembly 400. The preferred powersupply assembly 100 accepts three-phase power as an input and outputs DCoutput power. Illustratively, the power supply assembly receivesthree-phase power input at 480 V_(rms) and outputs 48 V DC at up to2000A.

The power supply enclosure 200 provides the mechanical mountinglocations for the physical components within the power supply assembly100. The power distribution assembly 210 comprises mounting hardware anddevices, such as fuses and circuit breakers, for distributing power tosystems that will use the regulated DC power. The rectifier 300generates the regulated DC power from the AC input. And, the fanassembly 400 provides a mechanism for cooling components in the powersupply assembly 100.

As shown in FIGS. 1 and 2, the rectifier assembly 300 comprises aplurality of power supply units (PSUs) 1000 that are coupled together inparallel to generate the desired output current capacity. Shown in FIG.3 is a block diagram of a preferred PSU 1000. The preferred PSU 1000comprises an active three phase power factor corrector assembly (“3Φ PFCassembly”) 400, a DC/DC converter assembly 500, and a digital controlassembly (“DCA”) 600. In the embodiment illustrated, the 3Φ PFC assembly400 accepts three phase AC input power and generates DC output power.The DC/DC converter assembly 500 receives the unregulated DC outputgenerated by the 3Φ PFC assembly 400 and converts the unregulated DCoutput to a regulated DC output voltage. The DCA 600 receives inputsfrom the 3Φ PFC assembly 400 and the DC/DC converter assembly 500 andgenerates control signals for the 3Φ PFC assembly 400 and the DC/DCconverter assembly 500.

With reference to FIG. 4, the preferred 3Φ PFC assembly 400 comprisesthree PFC assemblies 410, one for each phase of the three phase inputpower source. In one embodiment, the output of each PFC assembly 410 isprovided to a separate DC/DC converter 510. In an alternativeembodiment, as illustrated in FIG. 5, the output of all three PFCassemblies 410 within a 3Φ PFC assembly 400 are coupled together inparallel and provided to a single DC/DC converter 510. As illustrated inFIG. 6, each PFC assembly 410 preferably comprises a power factorcorrection circuit 2000, a coupled inductor 3000 having an adjustablecoupling factor, and a phase controlled inrush limiting circuit 4000.

It is to be understood that the components, circuits, systems andmethods described herein do not have to be implemented together. Manynovel features that may be implemented in power systems are describedherein. The novel features may be implemented separately or incombination with other novel features described herein.

Power Factor Correction Circuit 2000

As illustrated in FIG. 7, the preferred power factor correction circuit2000 comprises a power circuit 2100, a control circuit 2200 and a switchdrive circuit 2300. The control circuit 2200 monitors the power circuit2100 and controls the switch drive circuit 2300 to adjust the output ofthe power circuit 2100.

FIG. 8 provides a more detailed block diagram of the preferred powerfactor correction circuit 2000. The power circuit 2100 comprises aninput bank 2102 that includes a first input bank circuit 2104 and asecond input bank circuit 2106. The first and second input bank circuits2104 and 2106 are symmetric about a bank node 2108.

The input bank 2102 is connected to an output bank 2110. The output bank2110 comprises a first output bank circuit 2112 and a second output bankcircuit 2114. The first and second output bank circuits 2112 and 2114are also symmetric about the bank node 2108.

A rectified AC input voltage is provided across input terminals 2103 and2105 of the first and second input bank circuits 2104 and 2106,respectively. A regulated DC output voltage is generated across theoutput terminals 2111 and 2113 of the first and second output bankcircuits 2112 and 2114, respectively. The input voltage provided acrossthe input terminals 2103 and 2105 is substantially balanced so that themagnitude of the voltage measured from the input terminal 2103 to thebank node 2108 is substantially equal to the magnitude of the voltagemeasured from the bank node 2108 to the input terminal 2105. Likewise,the voltage from the output terminal 2111 to the bank node 2108 issubstantially equal to the voltage from the bank node 2108 to the outputterminal 2113.

At the output bank 2110, the voltage between the output terminal 2111and bank node 2108 and between the bank node 2108 and the outputterminal 2113 is referred to as the half-bank voltage. The half-bankvoltage is approximately one-half the voltage between the outputterminals 2111 and 2113.

The control circuit 2200 monitors the regulated DC output voltage at theoutput terminals 2111 and 2113, the rectified input voltage at theterminals 2103 and 2105, and a current signal in the power circuit 2100.The control circuit 2200 preferably operates from a flying node 2202.The flying node 2202 is a node that is either connected to the bank node2108 or the output terminal 2113. Thus, the voltage on the flying nodeis either at the half bank voltage or the voltage at the output terminal2113. Accordingly, the magnitude of the voltage change of the flyingnode 2202 is equal to the magnitude of the half bank voltage.

The switch drive circuit 2300 receives a control signal from the controlcircuit 2200 and provides a drive signal to drive switches in the firstand second output banks 2112 and 2114. The switch drive circuit 2300also operates from the flying node 2202.

A more detailed schematic diagram of the power circuit 2100 is providedin FIG. 9. The power circuit 2100 comprises a symmetrical arrangement oftwo switches S2122 and S2124, two free wheeling diodes D2126 and D2128,a multi-winding inductor L2130 that preferably comprises inductor coilsL2132, L2134 and L2136, two input capacitors C2138 and C2140 connectedin series across a rectified line, and two series connected bankcapacitors C2142 and C2144. A current sensing resistor R2146 ismonitored by the control circuit 2200.

The circuit of FIG. 9 is symmetric about the bank node 2108. A rectifier2148 receives an AC input and provides a rectified voltage that isdivided evenly above and below the bank node 2108. Thus, the voltagesacross the capacitors C2138 and C2140 are substantially equal. Balancingacross the bank node is described in further detail below. The rectifier2148 could be a standard rectifier known to those skilled in the art oralternatively the bridge circuit 4001 described herein in the InrushLimiting Circuit 4000 Section.

Shown in FIG. 9A is a preferred switch that can be used as switchesS2122 and S2124. The preferred switch comprises IGBT Q2150 coupled to abase resistor R2152. The preferred switch receives input signals fromthe switch drive circuit 2300 and changes states in response thereto.Alternative switches may be realized by using MOSFETs, BJTs, or otherswitching devices.

The state of the switches S2122 and S2124 determines the voltage of theflying node 2202. When the switch S2124 is in an open state, the diodeD2128 conducts and thus the flying node 2202 is at a voltage equal tothe voltage at the output terminal 2113. When the switch S2124 is aclosed state, the diode D2128 does not conduct and the voltage at theflying node 2202 is equal to the half-bank voltage at the node 2108.Therefore, the flying node 2202 has a voltage swing at an operatingfrequency of the control circuit 2200. The magnitude of the voltage isapproximately equal to the half-bank voltage.

The control circuit 2200, as illustrated in FIG. 10, utilizes acontroller A2204. An exemplary controller A2204 is a Unitrode/TexasInstruments UCC28180DW BiCMOS Power Factor Preregulator. The flying node2202 connected to Pin 1 of the controller A2204 switches at theoperating frequency of the power factor correction circuit 2200 at aswitched magnitude equal to the half-bank voltage. In the illustrativeembodiment of FIGS. 8-11, the half-bank voltage is 400V and theoperating frequency is 100 kHz. The supply voltage VCCP1 likewise fliesat 400V, 100 kHz, and is referenced from the flying node 2202.

Aside from the flying node 2202, the circuitry connected to pins 1, 2,3, 4, 5, 7, 8, 9, 10, 12, 13, 14, and 15 is substantially similar to thecircuitry connected to the controller when using a ground instead of theflying node 2202, as recommended by the manufacturer of the controllerA2204. Accordingly, only the circuitry connected to pins 6, 11, and 16is discussed in detail below.

Pin 11 references a bank voltage signal measured from output terminals2111 and 2113. Because the flying node 2202 is flying at 400V, 100 kHz,a difference amplifier A2206 is used to obtain the bank voltage signal.The difference amplifier A2206 includes a resistor R2208 and a capacitorC2210 connected in parallel between the inverting input and the outputof the amplifier A2206. Similarly, a resistor R2212 and a capacitorC2214 are connected in parallel between the non-inverting input and theflying node 2202.

A bypass capacitor C2216 may also be added between the inverting andnon-inverting inputs for added stability or noise rejection. A firstresistor R2218 connects the output terminal 2111 of the power circuit2100 to the non-inverting input of the difference amplifier A2206, and asecond resistor R2220 connects the output terminal 2113 of the powercircuit 2100 to the inverting input of the difference amplifier A2206.

The difference amplifier A2206 rejects the common mode component of the400V, 100 kHz signal, and provides a proportional amount of the outputvoltage of the power circuit 2100 through resistor R2222 to Pin 11 ofthe controller A2204.

Pin 6 of the controller A2204 receives a current signal that isproportional to the input voltage applied to the input terminals 2103and 2105. A resistor R2224 connects Pin 6 of the controller A2204 to theterminal L2136 a of the inductor coil L2136 (shown in FIG. 9). Theinductor coil L2136 bucks out the 400V, 100 kHz signal. The resistorR2224 converts the voltage signal appearing on the terminal 2136 a to acurrent signal. The voltage to be monitored and applied to the resistorR2224 is between the inductor coil terminals L2132 a and L2134 b. Bymeans of the inductor coil L2136, the voltage appearing between theinductor coil L2134 is cancelled. Thus, the voltage between the inductorcoil terminals L2136 a and L2134 a is essentially the same as thevoltage between the inductor coil terminals L2132 a and L2134 b.

Pin 16 of the controller A2204 is connect to the switch drive circuit2300 and provides a drive signal. A schematic diagram for the switchdrive circuit 2300 is shown in FIG. 11. The switch drive circuitincludes a driver A2302. An exemplary driver A2302 is an IR2110S HighAnd Low Side Drive, available from International Rectifier. The drivesignal from Pin 16 of the controller A2204 is provided to high side gatedrive input Pin 12 and the low side gate drive input Pin 14 of thedriver A2302, and thus the switches S2122 and S2124 are driven on andoff in unison.

The driver A2302 operates from the flying node 2202. Pin 6 of the driverA2302 is at the half-bank voltage, as it is connected to the bank node2108. Pin 8 provides a high side gate drive output signal to the coupledbases of the NPN-PNP paired transistors Q2310 and Q2312. The output ofthe paired transistors Q2310 and Q2312 drives the switch S2122.Likewise, Pin 1 provides a low side gate drive signal to the coupledbases of the NPN-PNP paired transistors Q2320 and Q2322. The output ofthe paired transistors Q2320 and Q2322 drives the switch S2124.

The power factor correction circuit 2200 enables power factor correctionfor high voltage inputs using switches S2122 and S2124, such as FETs orIGBTs, that in some embodiments are rated considerably less than thetotal output bank voltage. Furthermore, because the controller A2204 andthe driver A2302 operate from a flying node 2202, both the controllerA2204 and the driver A2302 dynamically adjust to receive the monitoringsignals from the power circuit 2100 and to provide the drive signals forthe switches S2122 and S2124.

During operation of the power factor correction circuit 2200, theswitches S2122 and S2124 are turned on and off simultaneously. Thevoltage at the input terminals 2103 and 2105 and at the output terminals2111 and 2113 is substantially balanced with respect to the bank node2108. The balancing of the voltage across the capacitors C2138 and C2140occurs when the switches S2122 and S2124 are closed. When these switchesclose, two symmetric circuits common to the bank node 2108 are created.The first symmetric circuit comprises a series connected input capacitorC2138, inductor coil L2132, and switch S2122. The second symmetriccircuit comprises a series connected input capacitor C2140, inductorcoil L2134, and switch S2124. In the second symmetric circuit, theimpedance of current sensing resistor R2146 is negligible, and thus thevoltage drop across this resistor is ignored. Thus, both symmetriccircuits essentially comprise a series connected capacitor and inductorcoil sharing a common node.

The coupling of the inductor coils L2132 and L2134 aids in the balancingof the input voltage across the input capacitors C2138 and C2140. Theinductor coils L2132 and L2134 are preferably a moderately coupledinductor device L2130. A preferred moderately coupled inductor is theinductor device 3000 which is described in further detail below in theCOUPLED INDUCTOR 3000 section. The coupling of the inductor coils L2132and L2134 causes the currents and voltages in each symmetric circuit tosubstantially match when the switches are closed. As coupling betweenthe inductor coils L2132 and L2134 is increased, the balancing of thevoltage across the capacitors C2138 and C2140 is increased. However,with very tight coupling between the inductor coils L2132 and L2134,transients in each symmetric circuit tend to increase when the switchesS2122 and S2124 close.

During the remaining time that the switches S2122 and S2124 are closed,energy is stored in the inductor L2130. The voltage applied across theinductor coils L2132 and L2134 is also equalized to the voltage acrossthe capacitors C2138 and C2140, respectively. The rate of the currentchanges in each inductor coil L2132 and L2134 also tends to be equal.

The switches S2122 and S2124 are turned off at the same time, creating afreewheeling interval for diodes D2126 and D2128. When the switchesS2122 and S2124 turn off, two symmetric circuits are created. The firstsymmetric circuit comprises a series connected input capacitor C2138,inductor coil L2132, diode D2126, and bank capacitor C2142. The secondsymmetric circuit comprises a series connected input capacitor C2140,inductor coil L2134, diode D2128, and bank capacitor C2144. In thesecond symmetric circuit, the impedance of current sensing resistorR2146 is negligible, and thus the voltage drop across this resistor isignored. Both symmetric circuits are symmetric about the bank node 2108.Additionally, the currents in both symmetric circuits at the moment theswitches S2122 and S2124 open are substantially equal.

In the first symmetric circuit, the voltage measured from the bank node2108 to the input terminal 2103 is positive. Energy stored in theinductor coil L2132 is released to the bank capacitor C2142 through thediode D2126. As the energy is released, the current decreases. Thus, themagnitude of output voltage across the output terminal 2111 and to thebank node 2108 is greater than the magnitude of the input voltage acrossthe input capacitor C2138.

In the second symmetric circuit, the voltage measured from the bank node2108 to the input terminal 2105 is negative. Energy stored in theinductor coil L2134 is released to the bank capacitor C2144 through thediode D2128. As the energy is released, the current decreases. Thus, themagnitude of output voltage across the output terminal 2113 and the banknode 2108 is greater than the magnitude of the input voltage across theinput capacitor C2140.

Accordingly, energy stored in the inductor L2130 when the switches S2122and S2124 are closed is released to the bank capacitors C2142 and C2144when the switches S2122 and S2124 are open. The interval that occurswhile the switches are open is the “freewheeling” interval. The voltagesacross the input capacitors C2138 and C2140 substantially match at thebeginning of the freewheeling interval, and the magnitude of the currentat the beginning of the freewheeling interval matches in the twofreewheeling diodes D2126 and D2128 and falls at substantially the samerate for each. Therefore the bank capacitors C2142 and C2144 receiveequal amp-seconds and thereby have matching voltages.

Shown in FIG. 12A is an alternative embodiment of the power circuit2100. This power circuit comprises a first coupled inductor havinginductor coils 2160 and 2162, and a second coupled inductor havinginductor coils 2170 and 2172. Inductor coils 2160 and 2170 store andrelease energy is a similar manner as described above with respect toinductor coils L2132 and L2134. Inductor coils 2162 and 2172 flowfreewheeling current through diodes D2164 and D2174, respectively, tobalance the voltage on the bank capacitors C2142 and C2144. Moderatelycoupling the inductor coils 2160 and 2162, and moderately coupling theinductor coils 2170 and 2172 aids in achieving the balancing across thebank node 2108 substantially as described above.

With reference to FIGS. 10 and 11, in another embodiment of the powerfactor correction circuit 2000, the ground Pin 1 of the controller A2204(and other circuitry in FIG. 10 coupled to Pin 1) is connected to theoutput terminal 2113 instead of the flying node 2202. Thus, the groundPin 1 does not fly at the half bank voltage as previously described.However, the COM Pin 2 of the driver A2302 remains referenced from theflying node 2202 and operates as previously described.

With reference to FIG. 12B, in another embodiment, the addition ofcurrent transformer 2154 between the switch 2124 and the flying node2202 and a second current transformer 2156 in series with diode D2128 atthe anode provides the current signal received by the controller A2204.The secondary windings of the current transformers are coupled to arectifier and summing device 2158 and summed into the resistor R2146,which is added is series between pins 4 and 2 of the controller A2204.Thus, the current sense resistor R2146 may be eliminated from the directpath in the power circuit 2100, and the controller A2204 may bereferenced from a ground rather than the flying node 2202. The switchesS2122 and S2124 may then be driven from gate transformers or opticalcouplers.

It is also to be appreciated that the switches S2122 and S2124 need notbe directly coupled to the switch drive circuit 2300. For example, gatetransformers or optical couplers may be used to drive the switches S2122and S2124. If gate transformers are utilized, the gate transformer forthe switch S2122 is referenced from the bank node 2108 and the gatetransformer for the switch S2124 is referenced from the flying node2202. If the switches S2122 and S2124 are switching devices actuated byan optical signal, the drive circuit may only be optically coupled tothe switches S2122 and S2124.

The power factor correction circuit 2100 thus may utilize semiconductordevices rated at one-half the output voltage across the output terminals2111 and 2113. Furthermore, the topology of the power circuit 2200inherently balances without a separate balancing control system.Finally, the power factor correction circuit 2100 may be combined withother power factor correction circuits 2100, thus providing for threesingle phase circuits to be combined to share a bank capacitor and asingle dc-dc converter load, as illustrated in FIG. 5.

Coupled Inductor 3000

The moderately coupled inductor device as previously described may bebetter understood with reference to FIGS. 13-18B. In particular, FIG. 13provides a schematic diagram illustrating a top view of an inductordevice 3000 having adjustable coupling between a first coil 3100 and asecond coil 3200. A first pair of inductor leads 3102 and 3104 isconnected to the first coil 3100, and a second pair of inductor leads3202 and 3204 is connected to the second coil 3200. The first coil 3100defines an outer periphery 3112 and an inner periphery 3114. Similarly,the second coil 3200 defines an outer periphery 3212 and an innerperiphery 3214.

A first C core 3300 includes legs 3302 and 3304, and a second C core3310 includes legs 3312 and 3314. Distal portions 3303, 3305, 3313 and3315 of the legs 3302, 3304, 3312 and 3314, respectively, are separatedby an air gap 3319. The air gap controls the reluctance of the magneticpath through the C core. An alternate method of controlling thereluctance is to use a lower permeability material for the C core andreducing or eliminating the air gap. The first coil 3100 is disposedover the C core legs 3302 and 3312, and the second core 3200 is disposedover C core legs 3304 and 3314. The first and second coils 3100 and 3200may be directly wrapped around the cores legs 3302, 3304, 3312 and 3314,or may be wrapped around plastic bobbins that slidably receive the corelegs 3302, 3304, 3312 and 3314.

Normally, in parallel disposition the first coil 3100 and the secondcoil 3200 on the opposite legs of the C cores 3300 and 3310 have veryloose coupling. However, the coupling between the first coil 3100 andthe second coil 3200 may be increased by adding a metal member 3400 thatextends around the outer periphery 3112 of the first coil 3100 and theouter periphery 3212 of the second coil 3200 to form a conductive loop.The metal member 3400 increases the magnetic interface between the firstcoil 3100 and the second coil 3200 to increase the resultant couplingbetween them. The first coil 3100 and the second coil 3200 areessentially coupled by transformer action through the metal member 3400.

The amount of coupling between the first coil 3100 and the second coil3200 for a given inductor structure with a fixed core size, fixed aspectratio, and fixed turns may be varied by changing the width, position,shape, the number metal members or the number of turns of metal membersextending around the outer peripheries 3112 and 3212. A wide range ofcoupling can be attained.

The metal member 3400 may comprise a single metal band extending aroundthe first and second outer peripheries 3112 and 3212 of the first andsecond coils 3100 and 3200. Alternatively, the metal member 3400 maycomprise metal sections connected by conductive wires, or may evencomprise a plurality of shorted conductor loops.

FIG. 14A provides a cross-sectional view of the inductor device 3000 ofFIG. 13. The first and second coils 3100 and 3200 are disposed over thefirst and second core legs 3302 and 3304 as previously described. Thecross-sectional view of FIG. 14A also shows that the first coil 3100defines top and bottom peripheries 3116 and 3118, and that the secondcoil defines top and bottom peripheries 3216 and 3218. The metal member3400 extends around the outer peripheries 3112 and 3212 and portions ofthe top and bottom peripheries 3116, 3118, 3216 and 3218 to form aconductive loop and thus couple the first and second coils 3100 and 3200by transformer action. The metal member 3400 may further follow thecontour of the first and second coils 3100 and 3200 closely aroundessentially the entire circumferences of the first and second coils 3100and 3200 to obtain maximum coupling.

Note that the thickness t of the metal member 3400 shown in FIG. 14A isexaggerated. Illustratively, if the metal member 3400 comprises a metalband, the thickness t of the metal member will be less than thethickness depicted in FIG. 14A.

FIG. 14B provides a cross-sectional view of the inductor device of FIG.13, in which the inductor device 3000 further includes insulationmaterial 3320 interposed between the first coil 3100 and core leg 3302,and insulation material 3330 interposed between the second coil 3200 andcore leg 3304. Furthermore, insulation material 3321 is interposedbetween the first coil 3100 and the metal member 3400, and likewiseinsulation material 3331 is interposed between the second coil 3200 andthe metal member 3400. The insulation material 3320, 3321, 3330 and 3331is provided to prevent shorting of the coils 3100 and 3200 to the corelegs 3302 and 3304, and to the metal member 3400. Furthermore, thethickness d of insulation material 3321 and 3331 may be selected toadjust the coupling of the first coil 3100 and the second coil 3200through the metal member 3400. Generally, as the thickness d of theinsulating material 3321 and 3331 increases, the coupling between thefirst and second coils 3100 and 3200 through the metal member 3400 willdecrease.

FIG. 14C is another embodiment of an inductor device 3000 havingadjustable coupling between the first coil 3100 and the second coil3200. The inductor device 3000 is substantially as described withrespect to FIG. 14A, except that the metal member 3400 comprises firstand second sections 3402 and 3412. The first section 3402 has distalregions 3404 and 3406 and is disposed around the outer periphery 3112and portions of the top and bottom peripheries 3116 and 3118 of thefirst coil 3100. The second section 3412 has distal regions 3414 and3416 and is disposed around the outer periphery 3212 and portions of thetop and bottom peripheries 3216 and 3218 of the second coil 3200. Thefirst and second sections 3402 and 3412 are connected by one or moreconductive wires 3422 and 3424 to form a conductive loop. The couplingbetween the first coil 3100 and the second coil 3200 when using thefirst and second sections 3402 and 3412 will be less than the couplingwhen using a continuous metal member 3400 as described with reference toFIG. 14A.

FIG. 14D provides another embodiment of an inductor device 3000 havingadjustable coupling between the first coil 3100 and the second coil3200. The embodiment of FIG. 14D is similar to the embodiment of FIG.14C, except that additional coupling is provided by a top metal member3430 that extends across portions of the top peripheries 3116 and 3216of the first and second coils 3100 and 3200, and a bottom metal member3440 that extends across portions of the bottom peripheries 3118 and3218 of the first and second coils 3100 and 3200. The distal regions3432 and 3442 of the first and second metal members 3430 and 3440 areconnected by one or more conductive wires 3452 adjacent the outerperiphery 3112 of the first coil 3100. Likewise, the distal regions 3434and 3444 of the first and second metal members 3430 and 3440 areconnected by one or more conductive wires 3454 located adjacent theouter periphery 3212.

While the embodiments of FIGS. 14C and 14D use conductive wires toconnect the sections of the metal member 3400 and thus form a conductiveloop, other conductive elements may be used, such as one or more metalbands.

FIG. 14E provides a top view of another embodiment of an inductor device3000 having adjustable coupling between a first coil 3100 and a secondcoil 3200. The embodiment of FIG. 14E is similar to the embodiment ofFIG. 14A, except that the metal member 3400 comprises a plurality ofshorted conductors 3460 extending around the outer peripheries 3112 and3212 and portions of the top and bottom peripheries 3116, 3118, 3216 and3218. The shorted conductors 3460 may be individually insulated. Theshorted conductors 3460 may also be enclosed in an insulating material3462 for added durability.

FIG. 14F is another embodiment of the inductor device 3000 havingadjustable coupling between the first coil 3100 and the second coil3200. The inductor device 3000 is substantially as described withrespect to FIG. 14A, except that the metal member 3400 defines distalregions 3404 and 3414 between the top peripheries 3116 and 3216. Animpedance element 3480 is connected between the distal regions 3404 and3414. The impedance element may have a complex impedance of the formZ=R+jX. The complex impedance may be realized by know devices, includingcircuits comprising capacitors, inductors, and resistors.

FIGS. 15, 16 and 17 provide front, top, and side views of an exemplaryinductor device 3000 that is constructed in accordance with theprinciples of the previously described embodiments. In the embodimentshown in FIGS. 15, 16 and 17, a plurality of metal bands 3400 a and 3400b extend around the first and second outer peripheries 3112 and 3212 ofthe first and second coils 3100 and 3200. The metal bands 3400 a and3400 b comprise steel bands wrapped around the inductor device andclamped by clamps 3401 a and 3401 b, respectively. Inductive couplingbetween the first coil 3100 and the second coil 3200 can be increased byadding additional bands 3400, or can be decreased by removing one orboth bands 3400 a and 3400 b. If additional metal bands 3400 are addedto increase coupling, the metal bands 3400 may be added along the outerperiphery 3112 and 3212 of the first and second coils, or may be addedaround the metal bands 3400 a and 3400 b to form layers of metal bands3400.

In addition to manufacturing of coupled inductor devices according tothe disclosed embodiments, it is to be appreciated that the coupling ofan existing coupled inductor may be adjusted by the relatively easy taskof adding one or more metal members 3400. Thus, the addition or removalof metal members 3400 provides for a quick and economical method andapparatus for adjusting the coupling between a first coil 3100 and asecond coil 3200 of an inductor device. Accordingly, an inductor devicehaving an initially loose coupling may be easily adjusted to have amoderate to tight coupling. This degree of coupling is preferable forcircuits such as the split inductor power factor circuit correctioncircuit 2000 described above.

While the embodiments of FIGS. 13-17 include two C cores 3300 and 3310,it is to be appreciated that other core arrangements may also be used,such as a single C core, a toroidal core, or other such cores used incoupled inductors. The cores may be constructed of steel, powdered iron,iron, ferrite, or other known core materials having high permeability.Additionally, the cores may further comprise insulated laminations toreduce eddy current losses.

Alternatively, the core may be constructed from a material with very lowpermeability, such as plastic, or the core may be eliminated. FIGS. 18Aand 18B provide front and top views of an inductor device 3000 with astandard air core and having adjustable coupling between the first andsecond coils 3100 and 3200. The first and second coils 3100 and 3200 arein parallel disposition and disposed on plastic tubular members 3470 and3472, which are in turn supported by plastic side members 3476 and 3478.The first and second coils 3100 and 3200 are then essentially twostandard air core inductors coupled only by their mutual inductance inair. Addition of a metal member 3400 increases the coupling between thefirst and second coils 3100 and 3200 as previously described.

Finally, while a metal member 3400 is preferred, it is to be appreciatedthat a synthetic member having a high permeability may also be used toincrease coupling between the first coil 3100 and the second coil 3200.Illustratively, one such synthetic member is constructed from a ceramicferrite material having a high electrical conductivity.

Another application of the inductor device 3000 is in conjunction with acurrent doubler circuit 3500, as shown in FIG. 19. The current doublercircuit 3500 includes a transformer 3510 comprising a primary winding3512 and a secondary winding 3514 wrapped around a transformer core3516. The inductor device 3000 is connected across the secondary winding3514, and is further connected to diodes D3100 and D3200, and to theoutput capacitor C3518. The power and control circuitry 3520 monitorsthe output of the current doubler circuit 3500 and switches the primaryvoltage V_(p) to the transformer 3510 to maintain a desired outputvoltage V_(o). The secondary voltage V_(s) switches in response to theswitching of the primary voltage V_(p).

When V_(s) is positive, D3100 is forward biased and D3200 is reversedbiased. Thus, current I₃₁₀₀ flows through D3100 and the output capacitorC3500, and current I₃₂₀₀ flows through D3100, the output capacitorC3518, and the secondary winding 3514 of the transformer 3510. WhenV_(s) is negative, D3100 is reversed biased and D3200 is forward biased.Thus, current I₃₁₀₀ flows through D3200, the output capacitor C3518, andthe secondary winding 3514 of the transformer 3510, and current I₃₂₀₀flows through D3200 and the output capacitor C3518. Thus, the outputcurrent I₃₅₀₀ is the sum of the two currents I₃₁₀₀ and I₃₂₀₀ flowingthrough the first and second inductor coils 3100 and 3200, respectively.

The inductive device 3000 utilized in the current doubler circuit 3500when the inductor coils are phased “bucking” provides for improvedfiltering of ripple on the output current I₃₅₀₀ versus that achievedusing individual inductors. When the inductor coils are phased “aiding”the inductive device 3000 reduces the AC inductive component of currentsupplied by the secondary winding 3514. Furthermore, the inductivedevice 3000 does not require sharing a common core with the transformer3510 to realize this improvement.

The inductor device 3000 is also preferable for other power circuits,such as a multiple output power supply in which a core shares windingsof inductors for the multiple outputs.

Inrush Limiting Circuit 4000

An inrush limiting circuit 4000, as illustrated in FIGS. 20A and 20B,comprises a silicon controlled rectifier (SCR) bridge circuit 4001, anSCR drive circuit 4100, a phased soft start circuit 4200, and a zerocross detection circuit 4300.

The SCR bridge circuit 4001 comprises first and second input terminals4002 and 4004 that receive an AC power source signal. The first inputterminal 4002 is connected to a diode D4012 and an SCR device,illustratively an SCR T4014. The second input terminal is connected tothe diode D4016 and SCR T4018. A first output terminal 4022 is connectedto SCRs T4014 and T4018, and the second output terminal 4024 isconnected to the diodes D4012 and D4016. The SCRs T4014 and T4018 areturned on and allowed to conduct by applying a short pulse to theirgates when a positive voltage is applied across their anode and cathode.Each SCR T4014 and T4018 turns off when a reverse voltage is appliedacross its anode and cathode.

The time beginning after the voltage across the anode and cathode of anSCR goes positive and continuing until the SCR is turned on is referredto as the phase delay. Increasing the phase delay reduces the outputvoltage across the output terminals 4022 and 4024. By selectivelydecreasing the phase delay from a large phase delay during an initialloading of the SCR bridge circuit 4001, the inrush current associatedwith various electrical devices when power is first applied can belimited, thus preventing damage to the electrical devices and excessiveinrush currents from the input power source.

The inrush limiting circuit 4000 controls the phase delay of the SCRsT4014 and T4018. The SCRs T4014 and T4018 are phase controlled duringpower up to limit the inrush current by introducing a large phase delayduring initial loading, and gradually decreasing the phase delay untilthe SCRs T4014 and T4018 remain fully phased on during normal operation.

During normal steady state operation the SCR drive circuit 4100 providesgate signals for turning on SCRs T4014 and T4018 substantially at thetime when the voltage across the anode and cathode of a particular SCRgoes positive. When the SCR drive circuit 4100 is enabled, the SCRsT4014 and T4018 are fully conducting and maximum power is provided tothe load or electrical device attached to output terminals 4022 and4024.

The phased soft start circuit 4200 phases in the SCR drive circuit 4100when a load or electrical device is coupled to output terminals 4022 and4024. The SCR drive circuit 4100 is initially disabled when power isapplied to the input terminals 4002 and 4004, and turned on after alarge phase delay is provided for the SCRs T4014 and T4018. The phasedsoft start circuit 4200 phases in the SCR drive circuit 4100, steadilydecreasing the phase delay until the phase delay is eliminated, at whichtime maximum power is provided to the load or electrical device coupledto output terminals 4022 and 4024.

The zero cross detection circuit 4300 monitors the AC input voltageapplied to the input terminals 4002 and 4004 for a zero crossing event.At the occurrence of a zero crossing event, the zero cross detectioncircuit 4300 provides a zero cross signal to the phased soft startcircuit 4200. The phased soft start circuit 4200 resets a phase delaysignal upon receiving the zero cross signal, which in turn increases theinstant phase delay of the SCRs T4014 and T4018.

Shown in FIG. 21 is a more detailed block diagram of an exemplaryembodiment of the inrush limiting circuit 4000. The zero cross detectioncircuit 4300 illustratively comprises a voltage divider 4302 and a pulsegenerator 4304. The voltage divider 4302 receives an AC power signal andoutputs a proportional amount of the signal. The pulse generator 4304monitors the voltage divider 4302 output and generates a pulse when thevoltage divider 4302 output is at or near zero volts.

The phased soft start circuit illustratively comprises a first phasesignal generator 4202 and a second phase signal generator 4204. Thesecond phase signal generator 4202 is periodically reset with each zerocrossing event detected by the zero cross detection circuit. The outputsof the first and second phase signal generators 4202 and 4204 are summedand a comparator 4206 compares the summed output signal to a referencevalue. Depending on the comparison, the SCR drive circuit 4300 is eitherenabled or disabled.

Shown in FIG. 22A is a schematic diagram of a preferred SCR drivecircuit 4100. Operation of the SCR drive circuit 4100 is explained indetail in U.S. Pat. No. 5,654,661, the disclosure of which isincorporated herein by reference, and to which the reader is referred toobtain a detailed understanding of the SCR drive circuit 4100. The SCRsT4014 and T4018 are driven with a current from the emitters of Q210 aand Q210 b, respectively. Added to the SCR drive circuit 4100 are leadsQBa and QBb. Lead QBa is connected to the base of the PNP transistorQ212 a, and lead QBb is connected to the base of PNP transistor Q212 b.The phase soft start circuit 4200 inhibits operation of the SCR drivecircuit 4100 by applying a voltage substantially equal to the supplyvoltage V_(cc) to the bases of the PNP transistors Q212 a and Q212 b.The transistors Q212 a and Q212 b are thereby shut off. Accordingly,transistors Q210 a and Q210 b cannot provide gate signals to the SCRsT4014 and T4018.

Shown in FIG. 22B is a schematic diagram of a preferred phased softstart circuit 4200 and the zero cross detection circuit 4300. DiodesD4210 and D4212 interface the phase control circuit 4200 to the gatedrive circuit 4100.

The PMOS transistor Q4214 functions as a comparator. The source of thetransistor Q4214 is at a voltage of V_(cc), and the gate of thetransistor Q4214 is at a voltage equal to the sum of the voltages acrosscapacitors C4216 and C4218. Thus, when the sum of the voltages acrossthe capacitors C4216 and C4218 and the gate threshold voltage of theTransistor Q42114 is less than V_(cc) the transistor Q4214 turns on.When the transistor Q4214 is on, V_(cc) is applied through the diodesD4210 and D4212 to the bases of the bases of the PNP transistors Q212 aand Q212 b, and the SCR drive circuit 4100 is inhibited as describedabove. When the transistor Q4214 is off (i.e., the sum of the voltagesacross the capacitors C4216 and C4218 and the gate threshold voltage ofthe transistor Q4214 is equal to or greater than V_(cc)), the SCR drivecircuit 4100 functions normally.

The voltages across the capacitors C4216 and C4218 provide first andsecond phase signals, respectively. The voltage across the capacitorC4218 is a periodic waveform that is reset at each zero crossing event,and is produced by injecting a first current I_(C4218) into thecapacitor C4218. The first current I_(C4218) is provided from a currentmirror formed by PNP transistors Q4220 and Q4222, and resistors R4224,R4226 and R4228. The resistor R4228 primarily determines the currentvalue of the first current I_(C4218) flowing from the collector oftransistor Q4222. The magnitude of the first current I_(C4218) ispreferably higher than the leakage current of the capacitor C4218.

A diode D4230 connects the collector of transistor Q4222 to thecollector of a phototransistor Q4232. When the phototransistor Q4232 isoff, the current I_(C4218) must flow through the capacitor C4218, as itis blocked by a diode D4234. When a zero crossing event occurs, thephototransistor Q4232 is turned on and the capacitor C4218 discharges,thus reducing its voltage. When the phototransistor Q4232 turns off, thevoltage across the capacitor C4218 begins to increase.

The voltage across the capacitor C4216 is a steadily rising ramp voltageproduced by the injection of the first current I_(C4218) and a secondcurrent I_(C4216). The second current I_(C4216) is provided from acurrent mirror formed by PNP transistors Q4220 and Q4236, and resistorsR4224, R4228, and R4238. The resistor R4228 primarily determines thecurrent value of the second current I_(C4216) flowing from the collectorof transistor Q4236. The magnitude of the sum of the first currentI_(C4218) and the second current I_(C4216) is preferably higher than theleakage current of the capacitor C4216.

Because the first and second currents I_(C4218) and I_(C4216) aredependent on V_(cc), and because the sum of the voltages across thecapacitors C4216 and C4218 is essentially compared to V_(cc),performance of the phased soft start circuit 4200 and phase-in the SCRdrive circuit 4100 is independent of the value of V_(cc).

An inhibit signal, SCR_INH, may also be applied to the gate of thetransistor Q4214 to inhibit the SCR drive circuit 4100. A controlcircuit may be configured to monitor the load or electrical deviceattached to the output terminals 4022 and 4024 and apply the inhibitsignal SCR_INH if a high inrush current or over-voltage condition isdetected.

As previously described, when the phototransistor Q4232 is turned on atthe detection of a zero crossing event by the zero cross detectioncircuit 4300, the voltage across the capacitor C4218 is reset to aninitial value and begins to increase as the capacitor begins recharging.The zero crossing detection circuit 4300 monitors the AC power signalthrough a voltage divider network comprising resistors R4310, R4312 andR4314. The resistor R4312 is a load resistor of a full wave rectifiercomprising diodes D4316, D4318, D4320, and D4322. Thus, the voltageacross the resistor R4312 is a full wave rectified voltage that isproportional to the AC power signal. Accordingly, when the voltageacross the resistor R4312 is at zero volts, a zero crossing event hasoccurred in the AC power signal.

The voltage across the resistor R4312 is applied to the zener diodesD4324 and D4326. A capacitor C4328 is connected in parallel with thezener diode D4324, which in turn has its cathode connected to the drainof a JFET transistor Q4330 through a resistor R4332 and LED D4334.Additionally, the anode of the zener diode is connected to the source ofthe transistor Q4330. Thus, when the transistor Q4330 is off, currentflow from the drain to the source is inhibited and the capacitor C4328charges up to the zener voltage of the diode D4324. When the transistorQ4330 is on, the capacitor C4328 discharges through the resistor R4332and LED 4324. Accordingly, the LED turns on the phototransistor Q4232and the voltage across the capacitor C4218 is reset.

The zero cross detection circuit 4300 is also self powered from thevoltage divider formed by resistors R4310, R4312 and R4314. Thus, aseparate supply voltage is not needed for the zero cross detectioncircuit 4300.

A zero crossing event is detected as follows. When the voltage acrossthe resistor R4312 is larger than a threshold voltage set by the sum ofthe voltage across zener diode D4324 and the threshold voltage of JFETtransistor Q4330, the transistor is off and no current will flow betweenthe drain and source. The gate of the transistor Q4330 will be reversebiased and protected by the zener diode D4326. When the voltage acrossthe resistor R4312 is smaller than the threshold voltage set by the sumof the voltage across zener diode D4324 and the threshold voltage ofJFET transistor Q4330, the transistor Q4330 turns on and beginsconducting current from the capacitor C4328 through the LED D4334. Thephototransistor Q4232 is thereby activated, and the voltage across thecapacitor C4218 is reset.

In the illustrative embodiment of FIG. 22B, the zero cross detectioncircuit 4300 is configured to activate the JFET transistor Q4330, andthereby activate the phototransistor Q4232, prior to the voltage acrossthe resistor R4312 actually reaching zero volts. Thus, the capacitorC4328 discharges slightly before the AC power signal actually reacheszero volts. By slightly anticipating the zero crossing event, the SCRdrive circuit 4100 is inhibited so as to prevent an SCR gate drivesignal from being present during or after the actual zero crossing ofthe AC power signal.

Accordingly, the zero crossing detection circuit 4300 may be configuredto have a zero crossing window. The size of the zero crossing window isdependent on the zener voltage of the zener diode D4324, the dividingratio of the voltage divider formed by resistors R4310, R4312, andR4313, and by the particular transistor Q4330. Design criteria may alsoinclude the propagation delay in the zero cross detection circuit 4300,the phased soft start circuit 4200, and the SCR drive circuit 4100. Ofcourse, the zero crossing window may be eliminated, and the inrushlimiting circuit may rely solely on line commutation of the SCRs T4014and T4018.

From the foregoing description, it is now understood that the transistorQ4214 is initially on when the inrush limiting circuit 4000 isactivated, thus inhibiting the SCR drive circuit 4100. The sum of thevoltages across the capacitors C4216 and C4218 is compared to a V_(cc)and the threshold voltage of the transistor Q4214. If the summed voltageacross the capacitors C4216 and C4218 exceeds V_(cc) minus the thresholdvoltage of the transistor Q4214, the transistor Q4214 is off and the SCRdrive circuit 4100 functions normally.

The voltage across the capacitor C4216 steadily rises to approximatelyV_(cc), at which time transistor Q4214 is fully off and the SCR drivecircuit functions normally. While the voltage across the capacitor C4216is rising, however, the voltage across the capacitor C4218 isperiodically rising and reset at each zero crossing event. Accordingly,the transistor Q4214 switches from an on state to an off state when thesummed voltage across the capacitors C4216 and C4218 exceeds V_(cc)minus the threshold voltage. When the voltage across the capacitor C4218is reset, the transistor Q4214 switches from an off state back to an onstate, inhibiting the SCR drive circuit 4100. As time progresses, theduration of the off state compared to the on state of the transistorQ4214 increases, until the transistor Q4214 is fully off. Thus, the SCRdrive circuit 4100 is phased in, and the inrush current associated witha load or electrical device is thereby limited.

By choosing the charging rate of the capacitors C4216 and C4218, thephase-in of the SCR drive circuit may be adjusted accordingly. Thecharge rate may be changed by adjusting the values of the capacitorC4216 and C4218, and also by adjusting the value of the resistors R4224,R4226, R4228, and R4238. In particular, R4228 may be made a variableresistor. Furthermore, by lengthening or decreasing the detection windowof the zero cross detection circuit 4300 as described above, thephase-in of the SCR drive circuit 4100 may be further adjusted.

Series Connected Full Bridge Circuit 5000

FIG. 23 provides a block diagram of a preferred series connected fullbridge circuit 5000. The series connected full bridge circuit 5000comprises an input stage 5100, a transformer stage 5200, and an outputstage 5300.

The series connect full bridge circuit 5000 provides for resonant powerconversion for soft switching. The input stage 5100 includes a firstbridge circuit 5102 and a second bridge circuit 5104, each of whichcomprise a plurality of switching elements that are AC coupled bycapacitors 5106. The first and second bridge circuits 5104 and 5106 aresymmetric about a bank node 5108. Input terminals 5107 and 5109 receivea DC input voltage wherein the first and second bridge circuits 5104 and5106 cause the bank node 5108 to be at a potential that is midwaybetween the potentials at the input terminals 5107 and 5109. Thus, theDC voltage measured from terminal 5107 to the bank node 5108 issubstantially equal to the DC voltage measured from the bank node 5108to terminal 5109.

The output of the first bridge circuit 5102 is provided to a firstprimary winding 5202 of the transformer 5200, and the output of thesecond bridge circuit is provided to a second primary winding 5204 ofthe transformer 5200. The first and second primary windings 5202 and5204 of the transformer are coupled by a coupled inductor 5208. Thecoupled inductor 5208 may be connected either on the primary side or thesecondary side of the transformer 5200. The output of the transformer5200 is center tapped and provided to the output circuit 5302. A DCoutput voltage is provided across the output terminals 5304 and 5306.

FIG. 24 provides a schematic diagram of a first embodiment of the seriesconnect split full bridge circuit 5000. The first bridge circuit 5102comprises a first switch S5110 and a second switch S5112. A diode D5116connects the input terminal 5107 and the collector of the switch S5110to a second terminal 5210 b of the first primary winding 5210. Thesecond terminal 5210 b is also directly connected to the collector ofthe second switch S5112. The emitter of the switch S5112 is connected tothe bank node 5108, and the emitter of the first switch S5110 isconnected to the bank node 5108 through diode D5118. Furthermore, theemitter of the first switch S5110 is also connected to the firstterminal 5210 a of the first primary winding 5210 through a firstwinding L5222 of a coupled inductor L5220. When the switches S5110 andS5112 are closed, an input voltage V_(IN) is applied across theterminals 5210 a to 5210 b of the first primary winding 5210.

The second bridge circuit 5104 is symmetric about the bank node 5108 tothe first bridge circuit 5102. The second bridge circuit 5104 comprisesa third switch S5130 and a fourth switch S5132. A diode D5136 connectsthe input terminal 5109 and the emitter of the third switch S5130 to asecond terminal 5212 b of the second primary winding 5212. The secondterminal 5212 b is also directly connected to the emitter of the fourthswitch S5132. The collector of the switch S5132 is connected to the banknode 5108, and the collector of the third switch S5130 is connected tothe bank node 5108 through diode D5138. Furthermore, the collector ofthe third switch S5130 is also connected to the first terminal 5212 a ofthe second primary winding 5212 through a second winding L5224 of thecoupled inductor L5220. When the switches S5130 and S5132 are closed, aninput voltage V_(IN) is applied across the terminals 5212 b to 5212 a ofthe second primary winding 5210.

The input capacitors C5140 and C5142 couple the bank node 5108 to theinput terminals 5107 and 5109, respectively. The DC input voltageapplied across the terminals 5107 and 5109 is evenly divided across theinput capacitors C5140 and C5142. The input capacitors C5140 and C5142are sufficiently large so that the DC voltage components do notappreciably change during a transition of the switches S5110, S5112,S5130 and S5132.

A first coupling capacitor C5144 bypasses the diodes D5118 and D5138 andprovides AC coupling of the emitter of the first switch S5110 to thecollector of the third switch S5130. Likewise, a second couplingcapacitor C5146 provides AC coupling of the collector of the secondswitch S5112 to the emitter of the third switch S5132. The couplingcapacitors C5144 and C5146 provide for tight AC coupling between theswitches S5110, S5112, S5130 and S5132 that occurs naturally in aconventional full bridge converter. The coupling capacitor C5144 iscoupled to the first terminals 5210 a and 5212 a through the coupledinductor L5220, and thus is charged to a DC voltage substantially equalto V_(IN). Similarly, the coupling capacitor C5146 is coupled to thesecond terminal 5210 b and 5212 b, and thus is charged to a DC voltagesubstantially equal to V_(IN). Preferably the coupling capacitors C5144and C5146 have capacitances that are greater than the capacitance of theswitches S5110, S5112, S5130 and S5132 so that the DC voltage componentof the coupling capacitors C5144 and C5146 does not appreciably changeduring transition of the switches S5110, S5112, S5130 and S5132. The DCblocking of the capacitors C5144 and C5146 thus enables the switches tobe split in separate bridges across the first and second primarywindings 5210 and 5212, and the AC coupling allows the switches tofunction as if they were directly connected in a full bridge.

The output circuit 5302 illustratively comprises diodes D5310 and D5312,an output capacitor C5314 and an output inductor L5316 configured as abuck converter output stage while a buck converter output stage isshown, other converter stages may be used, such as in boost converterstage. The first terminal 5214 of a first secondary winding 5214 isconnected to the output terminal 5304 and the output capacitor C5314through the diode D5310, and a second terminal 5216 b of a secondsecondary winding 5216 is connected to the output terminal 5304 and theoutput capacitor C5314 through the diode D5312. The second terminal 5214b of the first secondary winding 5214 is connected to the first terminal5216 a of the second secondary winding 5216. The output terminal 5306 isconnected to the second terminal 5214 b and the first terminal 5216 athrough the output inductor L5316.

Thus, when the switches S5110 and S5112 are closed and the switchesS5130 and S5132 are open, the diode D5310 is forward biased and currentflows from the first terminal 5214 a, through the diode D5310, throughthe output load and capacitor C5314, and returns through the inductorL5316. D5312 is reversed biased and does not conduct. Likewise, when theswitches S5130 and S5132 are closed, diode D5312 is forward biased andcurrent flows from the second terminal 5216 b, through the diode D5312,through the output load and capacitor C5314, and returns through theinductor L5316. D5310 is reversed biased and does not conduct.Therefore, current flow alternates between the two primary windings 5210and 5212, with current flowing in one of the primaries each half cycle.

While the switches S5110, S5112, S5130 and S5132 are illustratively IGBTdevices coupled to base resistors, alternative switches may be realizedby using MOSFETs, BJTs, or other switching devices. It is to beunderstood that the operation of the series connected full bridgecircuit 5000 takes into account the inherent parasitic capacitance ofthe particular device used to realize the switches S5110, S5112, S5130,and S5132. Accordingly, each switch S5110, S5112, S5130, and S5132 isthus bypassed by the inherent capacitance of the device used to realizedthe switch. Furthermore, depending on the capacitance of the switchingdevices used, separate bypass capacitors may also be added across theswitches to increase ZVS performance. The phantom capacitors C5110,C5112, C5130, and C5132 in FIGS. 24-26 are thus to be understood torepresent either the inherent parasitic capacitance of theircorresponding switches, or to represent separate parallel capacitors.

An exemplary controller for the switches S5110, S5112, S5130 and S5132is a UC3879 Phase-Shifted PWM Controller manufactured by UnitrodeCorporation/Texas Instruments. The UC3879 integrated circuit providescontrol, decoding, protection and drive functions for operation of aDC/DC converter with phase-shifted control. During operation of theseries connected split full bridge circuit 5000, the switches S5110,S5112, S5130 and S5132 are switched on and off according to thefollowing transition table:

Switch Switch S5110 Switch S5112 Switch S5130 Switch S5132 State StatusStatus Status Status 1 ON ON OFF OFF 2 OFF ON OFF OFF 3 OFF ON ON OFF 4OFF OFF ON OFF 5 OFF OFF ON ON 6 OFF OFF OFF ON 7 ON OFF OFF ON 8 ON OFFOFF OFF 9 ON ON OFF OFF

FIGS. 25A-25E provide the equivalent circuit diagram for the circuit ofFIG. 24 when the switches are in the Switch States 1-5, respectively.

During Switch State 1, shown in FIG. 25A, switches S5110 and S5112 areclosed, and an input voltage of V_(IN) is applied across the firstprimary winding terminals 5210 a and 5210 b. Accordingly, an equalvoltage is forced across the primaries 5212 a and 5212 b, as the primarywindings 5210 and 5212 share the same transformer core. A current I_(p)flowing through the first primary winding 5210 conducts through the path5400 as shown. Because the switches S5130 and S5132 are open, verylittle current flows through the second bridge 5104, and the capacitorsC5130 and C5132 are each charged to a magnitude of approximately V_(IN).Thus, the voltages on the first and second bridges 5102 and 5104 matchas in a conventional full bridge converter.

During the transition to Switch State 2, as shown in FIG. 25B, S5110 isturned off, and the voltage across the primary terminals 5210 a and 5210b rapidly collapses to zero. Likewise, the voltage across the primaryterminals 5212 a and 5212 b also collapses to zero. The output inductorL5316 provides energy to the output load through the current I_(L5316).The current I_(L5316) decreases as the inductor L5316 continues toprovide power to the output load. As the current I_(L5316) freewheelsthrough diode D5310, the primary current I_(p) is induced in the primarywinding 5210. However, as the voltage across the primary winding 5210collapses, the current I_(p) charges the capacitor C5110 up to a voltageof V_(IN). This causes the voltage across the capacitor C5130 todischarge to zero volts. Once the voltage across the open switch S5110is at V_(IN), the current I_(p) conducts through the diode D5118 andthrough the path 5402 as shown. The switch S5130 is then turned on whenthe voltage across the capacitor C5130 is at zero volts, resulting inthe equivalent circuit of FIG. 25C.

Switch S5112 is then turned off, resulting in the equivalent circuit ofFIG. 25D. During this transition, the coupled inductor L5220 providesenergy to induce the primary current I_(p). The current I_(p) chargesthe capacitor C5112 up to a voltage of V_(IN). Once the voltage acrossthe across the capacitor C5112 is at V_(IN), the current I_(p) conductsthrough the diode, D5116 and D5118, through the path 5404 as shown.Thus, the voltage across the capacitor C5112 is clamped to the voltageacross the capacitor C5146, which is equal to V_(IN). Therefore, thevoltage across the capacitor C5132 is at zero volts. The switch S5132 isthen turned on, resulting in the equivalent circuit of FIG. 25E.

Transition through the remaining Switch States 6-9 is substantiallysimilar to transition through Switch States 2-5, except that thepolarities of the voltages across the primary windings 5210 and 5212 arereversed. Thus, ZVS switching is provided for all switches S5110, S5112,S5130 and S5132.

It is to be appreciated that the windings L5222 and L5224 may also beseparate on separate inductors that are not coupled. However, this tendsto reduce the coupling between the transformer primary windings 5210 and5212 provided by the coupled inductor L5220, which impedes ZVSperformance. Thus, a coupled inductor L5220 comprising the windingsL5222 and L5224 is preferred. Illustratively, the windings L5222 andL5224 share a toroidal core and are tightly coupled.

An alternative embodiment is shown in FIG. 26. In this embodiment, thecoupled inductor L5220 is connected to the secondary windings 5214 and5216 of the transformer 5202. The first inductor winding L5222 isconnected between the first terminal 5214 a of the first secondarywinding 5214 and the diode D5310, and the second inductor winding L5224is connected between the second terminal 5216 b of the second secondarywinding 5216 and the diode D5312. ZVS switching occurs in the samemanner as described with respect to FIGS. 25A-25E.

Power Supply Unit and Control System

Shown in FIG. 27 is a block diagram of a preferred power supply unit(“PSU”) 7000 that comprises a plurality of power trains 7002, 7004, and7006 (three in this example) that receive AC input power and generate acombined DC output voltage. In the example shown in FIG. 27, each powertrain receives power from a different phase of a 3 phase AC powersource, but, in other embodiments some or all of the power trains couldreceive power from the same phase of a multi-phase AC power source, allof the power trains could receive power from a single phase AC powersource, or some or all of the power trains could receive power fromother AC power source configurations. The preferred PSU 7000 furthercomprises a combined control assembly (“CCA”) 7008 that preferably is adigital control assembly (“DCA”). The CCA 7008, among other things,takes power measurements from the output of each power train andgenerates control signals that are supplied to the power trains toaffect the output generated by each power train.

The power trains 7002, 7004, 7006 preferably are of similar architecturewherein each power train comprises a power factor correction (“PFC”)circuit 7010 and a DC/DC converter circuit 7012. The PFC circuit 7010could be of any suitable topology known by those skilled in the art suchas boost circuit, or alternatively could be of a configuration similarto the preferred PFC circuit 2000 described earlier in this detaileddescription.

The DC/DC converter circuit 7012 could be of any suitable topology knownby those skilled in the art such as a half bridge converter, full bridgeconverter, forward converter, resonant transition converter, PWMconverter, buck converter, boost converter, or other switching convertertopologies, or alternatively could be of a topology similar to thepreferred series connected full bridge circuit 5000 described earlier inthis detailed description. As illustrated in FIG. 28, the preferredDC/DC converter 7012 comprises a power generation circuit 7014 and acontrol circuit 7016. The power generation circuit 7014 preferablycomprises a switching circuit 7018, a transformer circuit 7020, and apower rectifier circuit 7022. The control circuit 70160 comprisescircuitry to generate control signals to drive switches in the switchingcircuit 7018 based, at least in part, on feedback from the powerrectifier circuit 7022.

Shown in FIG. 29 is a more detailed schematic of an exemplary powergeneration circuit 7014. The switching circuit 7018, comprises aplurality of switches, switch A, switch B, switch C, and switch D, thatare controlled by a control circuit 7016, which causes a regulated DCoutput to be generated at output terminals 7024, 7025. The powerrectifier circuit 7022 preferably includes a current sense circuit 7026that provides an output current signal I_(out) _(—) _(i) (e.g. I_(out)_(—) ₁, I_(out) _(—) ₂, or I_(out) _(—) ₃) that indicates the amount ofD.C. current the DC/DC converter 7012 provides to a load.

As illustrated in FIG. 30, each control circuit 7016 in the preferredPSU 7000 preferably is included in an overall PSU feedback loop. Thepreferred PSU feedback loop comprises the combined control assembly(“CCA”) 7008 and a control circuit 7016 for each power generationcircuit 7014. The CCA 7008 takes measurements from the output of eachpower generation circuit 7014 and measurements from the PSU's combinedD.C. output and generates error signals that are provided to eachcontrol circuit 7016. Each control circuit 7016, based on the errorsignals provided to it by the CCA 7008, generates control signals todrive the switches in the switching circuits.

A preferred control circuit 7016 is illustrated in FIG. 31. Thepreferred control circuit comprises an error signal conditioning circuit7028, a switch control signal generator circuit 7030, and a switchcontrol signal driver circuit 7032. The preferred error signalconditioning circuit 7028 receives a common error signal and a specificerror signal from the CCA 7008, combines the two error signals, andtransmits a combined error signal to the switch control signal generatorcircuit 7030. The common error signal is preferably a pulse widthmodulated (“PWM”) signal that represents the correction needed to drivethe overall output of the PSU to a desired level. The common errorsignal is a signal that is commonly provided to each control circuit7016. The specific error signal is preferably a PWM signal thatrepresents the correction that a specific power generation circuit 7014should make. Each specific error signal is specific to each controlcircuit 7016. A more detailed schematic of an exemplary error signalconditioning circuit 7028 is shown in FIG. 32 wherein the common errorsignal comprises ⁺V_(ERROR) and ⁻V_(ERROR), the specific error signalcomprises LDSHR_i, and the combined error signal comprises EA-.

As illustrated in FIG. 32, the preferred switch control signal generatorcircuit 7030 comprises a phase-shifted PWM controller 7034. In theembodiment shown, the phase-shifted PWM controller 7034 utilizes a UC3879 integrated circuit phase-shifted PWM controller. The phase-shiftedPWM controller 7034 generates control signals to drive switch A, switchB, switch C, and switch D in the associated power generation circuit7014.

Also, illustrated in FIG. 32 is the preferred switch control signaldriver circuit 7032. The switch control signal driver circuit 7032conditions the control signals generated by the switch control signalgenerator circuit 7030 so that the control signals can be coupled to theswitches in the associated power generation circuit 7014.

The CCA 7008 is preferably a digital control assembly (“DCA”) 7100 thatis illustrated in FIG. 33. The DCA 7100 preferably comprises a processorand more preferably a digital signal processor (“DSP”) 7102, althoughother processors such as a microprocessor or controller could be used.The preferred DSP 7102 is a DSP in the motor control class such as theTMS320LF2406. The DCA 7100 further comprises input conditioning circuits7104 and output circuits 7106. The input conditioning circuits 7104comprise circuits that measure characteristics relating to the PSU, suchas the PSU output voltage ⁺E_(out) and ⁻E_(out), the output currentI_(out) _(—) ₁, I_(out) _(—) ₂, and I_(out) _(—) ₃ provided by eachDC/DC converter, and the ambient temperature within the PSU, andgenerate output voltage representations of the characteristics that canbe sampled by the DSP 7102. The output circuits 7106, based at least inpart on processing occurring within the DSP 7102, the PSU output voltage^(+E) _(out) and ⁻E_(out), and the PSU output current I_(out) (whereinI_(out)=I_(out) _(—) ₁+I_(out) _(—) ₂+I_(out) _(—) ₃), generate thecommon error signal ⁺V_(ERROR) and ⁻V_(ERROR) and the specific errorsignals LSHR_1, LSHR_2 and LSHR_3 that are specific to each DC/DCconverter 7012.

The preferred input conditioning circuits 7104 include a HVS signalconditioning amplifier circuit 7108, an ambient temperature sensorcircuit 7110, and an output current conditioning circuit 7112. A moredetailed schematic view of an exemplary HVS signal conditioningamplifier circuit 7108 is shown in FIG. 34A, a more detailed schematicview of an exemplary ambient temperature sensor circuit 7110 is shown inFIG. 34B, and a more detailed schematic view of an exemplary outputcurrent conditioning circuit 7112 is shown in FIG. 34C. The HVS signalconditioning amplifier circuit 7108 converts the PSU output voltage⁺E_(out) and ⁻E_(out) to a proportional voltage level that can besampled by the DSP 7102. The ambient temperature sensor circuit 7110measures the ambient temperature within the PSU and provides a voltagethat is proportional to the PSU temperature to the DSP 7102. The outputcurrent conditioning circuit 7112 converts the output current from eachDC/DC converter to proportional voltages that can be sampled by the DSP7102.

With reference to FIGS. 33 and 34D, the DSP 7102 preferably includes ananalog-to-digital converter (“ADC”) section 7114 that is used to samplevoltages provided at inputs to the DSP 7102. The DSP 7102 executesalgorithms that cause it to perform computations using the sampledvoltages and allow the DSP 7102 to provide output signals to the outputcircuits 7106. Two of the output signals the DSP 7102 is preferablyprogrammed to generate are a digital current set point signal and adigital voltage set point signal. Other output signals include thespecific error signals LSHR_1, LSHR_2 and LSHR_3 that are utilized byeach DC/DC converter 7012 and two PWM signals PWM_7 and PWM_8 that areused for modulating the common error signal ⁺V_(ERROR) and ⁻V_(ERROR).

The preferred output circuits 7106 comprise a current referenceamplifier 7116, a voltage reference amplifier 7118, and a load sharingdriver circuit 7120. The current reference amplifier 7116 comprises adigital-to-analog converter (“DAC”) 7122 and converts the digitalcurrent set point signal provided by the DSP to an analog current setpoint signal IOSETPT that is used by other output circuits. The voltagereference amplifier 7118 also comprises a digital-to-analog converter(“DAC”) 7124 and converts the digital voltage set point signal providedby the DSP to an analog voltage set point signal VOSETPT that is used byother output circuits. The load sharing driver circuit 7120, asillustrated in FIG. 34E preferably comprises a plurality of gates 7126that provides the specific error signals LSHR_1, LSHR_2 and LSHR_3 thatare generated by the DSP with greater drive capability.

The preferred output circuits 7106 further comprise a current summingamplifier circuit 7128, a current shift amplifier circuit 7130, and acurrent error amplifier 7132. As illustrated by the exemplary embodimentin FIG. 34F, the current summing amplifier 7128 receives the voltagesignals generated by the output current conditioning circuit 7112 thatare representative of the output current I_(out) _(—) ₁, I_(out) _(—) ₂,and I_(out) _(—) ₃ provided by each DC/DC converter and sums the voltagesignals to produce an output voltage signal that is representative ofthe PSU output current I_(out). The output voltage signal that isrepresentative of the PSU output current signal I_(out) is transmittedto the current shift amplifier 7130 which further conditions the signaland transmits the conditioned signal to the current error amplifier7132, as illustrated in FIG. 34G. The current error amplifier 7132compares the conditioned PSU output current signal to the current setpoint signal IOSETPT. As the conditioned PSU output current signalincreases to a level at which it begins to exceed the current set pointsignal IOSETPT, the current error signal amplifier 7132 startsgenerating a current error signal I_(ERR) that causes the PSU outputvoltage ⁺E_(out) and ⁻E_(out) to decrease.

The preferred output circuits 7106 further include a voltage signalconditioning amplifier circuit 7134, a voltage error amplifier circuit7136, and a voltage error modulator circuit 7138. The voltage signalconditioning amplifier circuit 7134 receives the PSU output voltage⁺E_(out) and ⁻E_(out) and generates a conditioned representative voltagesignal that is transmitted to the voltage error amplifier circuit 7136.The voltage error amplifier circuit 7136 compares the conditionedvoltage signal to the voltage set point signal VOSETPT. As theconditioned representative PSU output voltage signal increases to alevel at which it begins to exceed the voltage set point signal VOSETPT,the voltage error amplifier circuit 7136 starts generating a voltageerror signal V_(ERR) that causes the PSU output voltage ⁺E_(out) and⁻E_(out) to decrease. The voltage error signal V_(ERR) is transmitted tothe voltage error modulator circuit 7138, which modulates the voltageerror signal V_(ERR) using a pair of complementary PWM signals PWM_7 andPWM_8 to generate the common error signal ⁺V_(ERROR) and ⁻V_(ERROR) thatis used by each DC/DC converter control circuit. An exemplary embodimentof the voltage error modulator circuit is shown in FIG. 34H. The voltageerror amplifier circuit 7136 also receives the current error signalI_(ERR), which is used to further adjust the voltage error signalV_(ERR).

The DSP 7102, therefore, has the ability to control the output of eachindividual DC/DC converter in the PSU through the generation of thespecific error signals LSHR_1, LSHR_2 and LSHR_3. The DSP 7102 also hasthe ability to control the overall PSU output through the generation ofthe current set point signal IOSETPT and the generation of the voltageset point signal VOSETPT.

Active AC Current Balance

The preferred PSU 7000 has the ability to actively balance the ACcurrent drawn amongst the power trains 7002, 7004 and 7006 in the PSU7000. To balance the AC current drawn by the power trains, the preferredPSU 7000 utilizes the DSP 7102 in the DCA 7100. The DSP 7102, throughthe generation of the specific error signals LSHR_1, LSHR_2 and LSHR_3,affects the level of output current I_(out) _(—) ₁, I_(out) _(—) ₂, andI_(out) ₃ provided by provided by each DC/DC converter circuit in thePSU 7000. After sampling the output currents I_(out) _(—) ₁, I_(out)_(—) ₂, and I_(out) _(—) ₃ provided by the current sense circuit 7026 ineach DC/DC converter, the DSP 7102 can generate appropriate specificerror signals LSHR_1, LSHR_2 and LSHR_3 that will cause each DC/DCconverter circuit 7012 in the PSU 7000 to generate an equal level ofoutput current I_(out) _(—) ₁, I_(out) _(—) ₂, and I_(out) _(—) ₃. Whenall of the DC/DC converters 7012 are generating an equal level of outputcurrent I_(out) _(—) ₁, I_(out) _(—) ₂, and I_(out) ₃, they will draw anequal level of current from the PFC circuits 7010 to which they arecoupled. If all of the PFC circuits 7010 are providing an equal level ofcurrent to the DC/DC converters 7012, then the PFC circuits 7010 willdraw an equal level of AC current from the AC supply assuming the ACvoltage is balanced in the AC supply. Consequently, by balancing theDC/DC converter output currents I_(out) _(—) ₁, I_(out) _(—) ₂, andI_(out) _(—) ₃, AC current balance can be achieved in the PSU 7000.

The preferred AC current balance circuit, therefore, comprises thecurrent sense circuit 7026 (shown in FIG. 29) in each DC/DC converter7012 and the circuitry within the DCA 7100 that generates the specificerror signals LSHR_1, LSHR_2 and LSHR_3. The DSP 7102 preferablygenerates the specific error signals LSHR_1, LSHR_2 and LSHR_3 throughits use of a current balancing algorithm 7200.

The preferred current sense circuit 7026 comprises a thevenin resistorR7027 that is coupled into the output path of the DC/DC converter 7012and associated circuitry that generates a current measurement that isproportional to the output current I_(out) _(—) _(i) flowing through theDC/DC converter.

The preferred current balance algorithm 7200, as illustrated in FIG. 35,instructs the DSP to compute the total PSU output current I_(out) bysumming the DC/DC converter output currents I_(out) _(—) ₁, I_(out) _(—)₂, and I_(out) _(—) ₃ wherein the total PSU output currentI_(out)=I_(out) _(—) ₂+I_(out) ₁₃ ₃ (step 7202). The average outputcurrent for each DC/DC converter I_(avg) is computed whereinI_(avg)=I_(out)/3 (step 7204). PWM signals (LSHR_1, LSHR_2 or LSHR_3)are generated wherein each PWM signal corresponds to a DC/DC converteroutput current signal I_(out) _(—) ₁, I_(out) _(—) ₂, and I_(out) _(—) ₃(step 7206). Each PWM signal preferably is initially a 150 Khz signalwith a 50% duty cycle. Each DC/DC converter output current signalI_(out) _(—) ₁, I_(out) _(—) ₂, and I_(out) _(—) ₃ is compared to theaverage output current for each DC/DC converter I_(avg) (steps 7208 and7209). If a DC/DC converter output current signal I_(out) _(—) _(i) isgreater than the average output current signal I_(avg), then preferablythe duty cycle of the corresponding PWM signal LSSHR_(—i) (whereinLSSHR_i=LSHR_1, LSHR_2 or LSHR_3) is decreased (step 7210) by anappropriate amount to cause the DC/DC converter output current todecrease appropriately. If a DC/DC converter output current signalI_(out) _(—) _(i) is less than the average output current signalI_(avg), then preferably the duty cycle of the corresponding PWM signalLSSHR_i is increased (step 7212) by an appropriate amount to cause theDC/DC converter output current to increase appropriately. For example,if I_(out) _(—) ₁ was 10% greater than I_(avg), I_(out) _(—) ₂ was equalto I_(avg) and I_(out) _(—) ₃ was 10% less than I_(avg), the duty cycleof LSHR_1 and LSHR_3 would be adjusted appropriately. The duty cycle ofLSHR_1 could be decreased 10% and the duty cycle of LSHR_3 could beincreased 10%. The amount of increase or decrease of the duty cycle canbe determined by one of ordinary skill in the art. Preferably thecurrent balance algorithm is executed once per second to adjust the PWMsignals (LSHR_1, LSHR_2 and LSHR_3).

Adaptive Control Circuit

The preferred DCA 7100 preferably functions as an adaptive controlcircuit 7300 as illustrated in FIG. 36A. For example, when used with atelecom rectifier the adaptive control circuit 7300 adaptively controlsa PSU 7000 by preferably monitoring input such as the PSU input voltage,ambient temperature in the PFC and DC/DC converter circuits, individualcomponent temperatures, plant size (amp-hour rating of batteries), PSUoutput voltage and PSU output current to optimize the PSU's controlalgorithms.

As illustrated in FIGS. 36A and 36B, the adaptive control circuit 7300comprises the DSP 7102 in operation with a plurality of controlalgorithms. Preferably the control algorithms include a voltage loopcontrol algorithm 7302 in which output load current, temperature, andbattery plant size are control variables, an extended rechargecapability control algorithm 7304, and a brown-out/black-out controlalgorithm 7306, as shown in FIG. 37.

The voltage loop control algorithm 7302 eliminates closed loopinstability in a rectifier such as the PSU 7000 that can occur, forexample, due to the different size battery plants that can be applied tothe rectifier, changes in ambient temperature, and changes in outputload current. The voltage loop control algorithm 52 preferably addsinputs for plant size, output current, and ambient temperature into thevoltage loop computation in addition to the output voltage input. Addingthese inputs can prevent the rectifier from becoming unstable underextreme temperature, load, and/or plant size situations.

The extended recharge capability control algorithm 7304 can adjust themaximum output current of the PSU 7000 to beyond the nominal ratingpreferably depending on the ambient temperature. This greatly reducesthe time or number of PSUs 7000 needed to recharge batteries in a powersystem. The extended recharge algorithm 54 preferably monitors theambient temperature in a select number of individual components andadjusts the maximum allowable output current to a level beyond thenominal rating of the rectifier if the ambient temperature is below athreshold. For example, in a tightly controlled environment, such as acentral office, a 200 AMP rectifier could provide 250 or 275 Amps in abattery recharge situation. The DSP could accomplish this by increasingthe current set point value by an appropriate amount. This would reducethe number of rectifiers needed and/or the time required to recharge thesystem's batteries.

The brown-out/black-out control algorithm 7306 allows the PSU to operateat a reduced output current level when the AC input voltage is below thenominal voltage range. This will allow the PSU 7000 to supply some ofthe load during a low AC input voltage condition thereby reducing oreliminating battery discharge. The brown-out/black-out control algorithm7306 preferably monitors the input voltage and reduces the maximumoutput current of the rectifier based on the input voltage. This allowsa power system to provide some power where existing systems would haveshut down due to, for example, input voltages that are too low. Forexample, the DSP can accomplish this by reducing the current set pointvalue by an appropriate amount if the input AC voltage is below athreshold level.

Conclusion

Other variations from these systems and methods should become apparentto one of ordinary skill in the art without departing from the scope ofthe invention defined by the claims. The embodiments described hereinand shown in the drawings are examples of structures, systems or methodshaving elements corresponding to the elements of the invention recitedin the claims. This written description and drawings may enable thoseskilled in the art to make and use embodiments having alternativeelements that likewise correspond to the elements of the inventionrecited in the claims. The intended scope of the invention thus includesother structures, systems or methods that do not differ from the literallanguage of the claims, and further includes other structures, systemsor methods with insubstantial differences from the literal language ofthe claims. Although some of the embodiments have been described withreference to a telecommunication rectifier, it is understood that theinvention is applicable to other power systems. It is also to beunderstood that the invention is not limited to use with atelecommunication rectifier unless explicitly limited by the claims.

1. A DC/DC converter, comprising: first and second bridges, each firstand second bridge comprising a plurality of switch elements; a pluralityof coupling capacitors, each coupling capacitor coupling one of theswitch elements of the first bridge to one of the switch elements of thesecond bridge; a transformer comprising a first primary winding, asecond primary winding, and a secondary winding, each of the firstprimary winding and the second primary winding defining first and secondterminals, the first primary winding connected to the first bridge, andthe second primary winding connected to the second bridge; and a coupledinductor comprising first and second inductors, the coupled inductorconnected to the transformer so that the first and second primarywindings are inductively coupled through the coupled inductor.
 2. TheDC/DC converter of claim 1, wherein the secondary winding of thetransformer comprises a first secondary winding and a second secondarywinding, each of the first secondary winding and the second secondarywinding defining first and second terminals, the second terminal of thefirst secondary winding connected to the first terminal of the secondsecondary winding to form a secondary node.
 3. The DC/DC converter ofclaim 2, further comprising a third inductor, the third inductorconnected to the secondary node.
 4. The DC/DC converter of claim 3,further comprising: a first bridge capacitor connected in parallel withthe first bridge; and a second bridge capacitor coupled in parallel withthe second bridge.
 5. The DC/DC converter of claim 4, wherein the firstinductor is interposed between the first terminal of the first primarywinding and the first bridge, and the second inductor is interposedbetween the first terminal of the second primary winding and the secondbridge.
 6. The DC/DC converter of claim 4, wherein the first inductor isconnected to the first terminal of the first secondary winding and thesecond inductor is connected to the second terminal of the secondsecondary winding.
 7. The DC/DC converter of claim 1, wherein theswitching elements are IGBT devices.
 8. The DC/DC converter of claim 1,wherein the switching elements are MOSFET devices.
 9. A DC/DC converter,comprising: a first bridge comprising first and second switches andfirst and second diodes, the first bridge defining a first node and asecond node, the first switch and the first diode series connectedbetween the first and second nodes, and the second switch and seconddiode series connected between the first and second nodes; a secondbridge comprising third and fourth switches and third and fourth diodes,the second bridge defining the second node and a third node, the thirdswitch and the third diode series connected between the second and thirdnodes, and the fourth switch and fourth diode series connected betweenthe second and third nodes; a first capacitor connected between thefirst and third switch; a second capacitor connected between the secondand fourth switch; a transformer comprising a first primary winding, asecond primary winding, and a secondary winding, each of the firstprimary winding and the second primary winding defining first and secondterminals, the first terminal of the first primary winding connected tothe second switch and second diode, and the first terminal of the secondprimary winding connected to the fourth switch and fourth diode; and acoupled inductor comprising first and second inductors, the coupledinductor connected to the transformer so that the first and secondprimary windings are inductively coupled through the coupled inductor.10. The DC/DC converter of claim 9, wherein the first inductor isconnected between the second terminal of the first primary winding andthe first switch, and the second inductor is connected between thesecond terminal of the second primary winding and the third switch. 11.The DC/DC converter of claim 10, wherein the secondary winding of thetransformer comprises a first secondary winding and a second secondarywinding, each of the first secondary winding and the second secondarywinding defining first and second terminals, the second terminal of thefirst secondary winding connected to the first terminal of the secondsecondary winding to form a secondary node.
 12. The DC/DC converter ofclaim 11, further comprising a third inductor, the third inductorconnected to the secondary node.
 13. The DC/DC converter of claim 12,further comprising: a first bridge capacitor connected in parallel withthe first bridge; and a second bridge capacitor coupled in parallel withthe second bridge.
 14. The DC/DC converter of claim 13, wherein theswitching elements are IGBT devices.
 15. The DC/DC converter of claim13, wherein the switching elements are MOSFET devices.
 16. The DC/DCconverter of claim 9, wherein the second terminal of the first primarywinding is connected to the first switch and first diode, and the secondterminal of the second primary winding connected to the third switch andthird diode.
 17. The DC/DC converter of claim 16, wherein thetransformer secondary winding comprises a first secondary winding and asecond secondary winding, each of the first secondary winding and thesecond secondary winding defining first and second terminals, and thefirst inductor is connected to the first terminal of the first secondarywinding and the second inductor is connected to the second terminal ofthe second secondary winding.
 18. The DC/DC converter of claim 17,wherein the second terminal of the first secondary winding is connectedto the first terminal of the second secondary winding to form a fourthnode.
 19. The DC/DC converter of claim 18, further comprising a thirdinductor, the third inductor connected to the fourth node.
 20. The DC/DCconverter of claim 19, further comprising: a first bridge capacitorconnected in parallel with the first bridge; and a second bridgecapacitor coupled in parallel with the second bridge.
 21. The DC/DCconverter of claim 20, wherein the switching elements are IGBT devices.22. The DC/DC converter of claim 20, wherein the switching elements areMOSFET devices.
 23. A method of DC/DC conversion in a DC/DC convertercomprising first and second bridges and a transformer comprising a firstprimary winding, a second primary winding, a first secondary winding,and a second secondary winding, comprising the steps of: capacitivelycoupling the first and second bridges with coupling capacitors; andinductively coupling the first and second primary windings with coupledinductors.
 24. The method of claim 23, wherein the step of inductivelycoupling the first and second primary windings with coupled inductorscomprises the steps of: connecting the first primary winding to a firstinductor; and connecting the second primary winding to a secondinductor; wherein the first and second inductors are inductivelycoupled.
 25. The method of claim 24 wherein the step of inductivelycoupling the first and second primary windings with coupled inductorscomprises the steps of: connecting the first secondary winding to afirst inductor; and connecting the second secondary winding to a secondinductor; wherein the first and second inductors are inductivelycoupled.
 26. The method of claim 22, wherein the step of capacitivelycoupling the first and second bridges with coupling capacitors comprisesthe steps of: coupling a first switch in the first bridge to a firstswitch in the second bridge with a first capacitor; and coupling asecond switch in the first bridge to a second switch in the secondbridge with a second capacitor.
 27. A power system comprising aplurality of power supply units (“PSUs”), each PSU having an output thatis coupled to the output of other PSUs in the power system, each PSUcomprising: a power factor correction (“PFC”) assembly for receiving anAC input and generating a first DC output; a DC/DC converter assemblythat is coupled to the PFC assembly, the DC/DC converter assemblyreceiving the first DC output and generating a second regulated DCoutput, the DC/DC converter comprising: first and second bridges, eachfirst and second bridge comprising a plurality of switch elements; aplurality of coupling capacitors, each coupling capacitor coupling oneof the switch elements of the first bridge to one of the switch elementsof the second bridge; a transformer comprising a first primary winding,a second primary winding, and a secondary winding, each of the firstprimary winding and the second primary winding defining first and secondterminals, the first primary winding connected to the first bridge, andthe second primary winding connected to the second bridge; and a coupledinductor comprising first and second inductors, the coupled inductorconnected to the transformer so that the first and second primarywindings are inductively coupled through the coupled inductor; a controlassembly that is coupled to the DC/DC converter assembly, the controlassembly being operative to monitor the DC/DC converter assembly outputand in response thereto to provide control signals to the DC/DCconverter assembly, the control assembly comprising, a plurality ofcontrol assembly input circuits, the control assembly input circuitsbeing operative to measure characteristics relating to the DC/DCconverter assembly and operative to generate a measured characteristicsoutput; a signal processor having a signal path to the control assemblyinput circuits, the signal processor being operative to receive themeasured characteristics output, perform computations wherein themeasured characteristics output is used in the computations, andgenerate a signal processor output; and a plurality of control assemblyoutput circuits, the control assembly output circuits being operative togenerate error signals based on the signal processor output.